Telephone trunking system.



IMJ

MWI/555.55

9, n.. n l Y I M/W TTOH/I/ES/ E. D. PALES- TELEPHUNE THUNKING SYSTEM. APPUCATION FILED MAR.30.1909.

PamutedJuue 22, 1915i 5 sHETs-sHEEfz.

.Mw @NNN WUs/555.55 2M E. D. FALES.

TELEPHONE TRUNKING SYSTEM.

APPucATmN FILED r11/111.30. 1909.

1,143,820. Patented J une 22, 1915.

5 SHEETS-SHEET 3.

TTO/P/VEYS,

E. D. FALES.

TELEPHONE TRUNKING SYSTEM.

ARH-NATION FILED MAR. 30 |909. 1,143,820. Patented June 22, 1915 5 SHEETS-SHEET 4.

/N `7^ TTOR/VEYS,

E. D; FALES. v TELEPHONE TRUNKING SYSTEM. APPLICATION mso MAR. 30. 1909.

1,143,820. Patented June 22, 1915.

5 SHEETS-SHEET 5.

imam/5X5.

saires Parana* sich.

EDW'ABD D. FADES, 0F LA GRANGE, ILLINQIS, TOVATOMATIC ELEGTRIG CGMPNY, 0F CHICAGO, IILLINOIS, A CORPGRATION GF ILLINOIS.

TELEPHONE 'rnUNKruG SYSTEM.

speciacauon of Leiters Patent.

. Patented June 22, 1915.

.reputation and maren so, 190s. seran nu. scares.

y To all wky'm it may concern Be it lnown that I, EnwARD D. Flinn-s, a citizen of the United States of America, and resident of La Grange, Cook county, Illinois, have invented a certain new and useful Improvement in Telephone Trunking Systems, of which the following .is a speciiication.

My invention relates vto automatic telephone systems in general, for example, automatic telephone systems in which switches of the Strowger type are employed, such as vselectors and connectors of the general type shown and described in United States Letters Patent llos. 815,321 and 815,176, issued March 13, 1906, to Keith, Erickson and Erickson; and is especially1 applicable to au tomatic telephone systems in which switches of the so-called Keith type are'also employedv My invention is applicable Where Keithswitches are used individual to each subscriberls line, and where they are used as .secondary switches-that is, Where they are used for the purpose of making all of the numerical switches of a certain denominay tiii, such as second selectors, common to all of the subscribers of an exchange, or common to more than one group of one hundred subscribers, as far example, common to a number of groups of the so-called Keith units.

More particularly, my invention relates to systems employing Keith switches of the kind -that are controlled by a common mechanism linown as the master switch, which master switch is designed to select the next idletrunk to be used by the next calling subscriber as soon as a subscriber has made a call, and which, While thus operating to find the next idle trunlr line,- prevents any subscriber from operating his line switch until themster switch cornes to a standstill. The

'Keith switches aforesaid may be ofthe character which are normally ready, at any instant that .the master switch 4is still, to seize a preselected idle trunk when a subscriber 5 removes his receiver, and thusconnect the calling line with V e preselected idle trunk. i One objection heretofore-has been that if two or more subscribers remove their receivers while the master switch ismoving, the

individual switches oil these subscribers who have thus removedtheir receiverswill op.-v

erate simultaneously at the instant that the master switch stops and seize the same trunk.

Objects of my invention are, therefore, to provide means whereby the line switch of a subscriber who removes hisreceiverwhile the master switch is moving will be locked and so retained until the subscriber releases, said subscriber, of course, not getting a number until he calls again; to provide means whereby a subscriber who has been thus locked by attempting to call while the master switch is moving is enabled to release and restore his apparatus to norma-l upon receiving the busy signal, whereby he may make a call after releasing; to provide means whereby secondary switches' which are seized 'while the. master switch controlling the saine is moving may also be lockedv in connection with the busy signal apparatus, same as the vline switches; to provide means whereby a subscriber who, having seized a secondary switch and been thus locked on the busy apparatus, may release.

and restore the apparatus he has brought into use, so that another call may subsequently be made; and to provide other features of improvement tending to increase the eliciency andserviceability of an automatic telephone system.

To the foregoing and other useful ends, my invention consistsin matters hereinafter set forth and claimed.

In theaccompanying drawings, which are. a. part of this' specification, Figure l is a` diagrammatic representation of a circuit established through apparatus of the character described by a calling subscriber A. The

one hundred, for example,all oiwhic may. be controlled by a commen master switch current for establishing this connection is i of the master switch D, located between the said master switch and the busy coil, is not a part of the master switch, but is individual to the subscriber A. After passing through No. 1,110 are shown. The general modeof the line switch C the circuit is shown extending through the so-called firstselectoi' FJ. l

Fig. 2 is likewise a diagram, showing aV continuation of the circuit shown in Fig. 1. Said circuit is shown passing through a secondary switch F,.which is also oneA of a 'group of similar switches. It may be well to call attention to the fact that these circuits are shown returning to battery B by Way of the grounded terminal G; but this, of course, is not a necessary arrangement, and battery B need not be grounded at all. The secondary switch F, as well as all of the remaining secondary switches of the same group, may be controlled 'by the master switch H. It should vbe stated that 'the switches which a master switch may control need not be a definite number; one master switch may, for example, be arrangedto control only twenty-live switches, orcnly fiftyswitches, or any other number which may be convenient. After passing through the* secondary switch F in Fig. 2 the circuit 1sl shown selector'I.

Fig. 3 is also a diagram, and shows an extension of the circuits after passing through Fig.' 2. This circuit, it will be seen, extends irst to the switch J, known as a connector switch, thence through the line switch C. of the called' subscriber, and vthen to the called subscriber` K. It .will be obvious, of course, that' thefline switch C may bel a line switch of the same group as the line switch C, in which case it would be controlled by the master'switch D. .It is as! sumed, however, for convenience of illustration, that the switches C and C do not belong to the same group, and are, therefore, not controlled by the same master switch. The only part of the controlling master switch of the line switch C shown is the relay L. The switches C and C are, of course,`the same in all respects.

Fig. 4'is a simplified diagram illustratpassing through the second -ing all of the switches in a ten thousand system. In this ligure, 3 is intended to represent ten, and three groups of three is intended to represent ten times ten, or one hundred. On Kthis sheet the calling subscriber- No. 10,091 and the called subscriber operation ofthe line and master switches is\ similar to that described in the Western Electrician of Chicago of January 11, 18

and25, 1908. The general operation ofthe secondary switchesv is quite similar to that o 'ffthe line switches, and the general opera- -tionof theselectors and connectors is quite well-known. The general mode of operai. tion of the line switches is also described in British Patent No. 26,301 of 1906.

Fig. 5 illustrates diagrammatically the l '10 essential mechanical features of the master switch D shown inFig. 1.

Fig. 6 is a modification of the circuits of i the master switch D shown in Fig. 1.

In the particular form of. line switch herein illustrated the usual plunger is carried upon the end ofthe plunger arm 26 which is controlled by the magnet 250. This 3 magnet also controls the two relay arma n 'y tures 18 and 35, and comprises four windings, namely, a pull-in winding 20, a cut-off winding 51, a line winding 8 and an aux iliary windingI 21. Owing to the fact that the core of the magnet 250 is attached near the center of its length to the bracket 252, to which latter are pivoted the armatures 26,

windings 21 and 8. .With this arrangement-V the armatures on the upper en d of the mag-` net are not aiiected by the windings on 'the'.

Alower end, and viceversa. Of the two wind- 'f 'ings on the upper end of the magnet the winding 20 is the stronger and, when'en" ergized, operates both the plunger arm 2611i -l 9,5?

and the armature 35. The winding 51 is not strong enough to attract the plunger arm 26 from its ,normal position, but will I hold it in its operated position after it has:

once been pulled down by the windingu20.

My invention is illustrated in the draw;k l ings in combination with a two-wire sys-l tem, and when the calling subscriber re-` i moves his receiver he disconnects his bell 2r from across the line and closes the `line cir'-- cuit through the springs 3 and 4. The calulY ing device at the' telephone isthe ordinary automatic calling device usediin connection. with the Strowger system and apparatus'of the general character already described.y

lhere is this diiierence howeverythat the` impulse wheel 5, instead of operating to closeacircuit intermittently as it returns Y toward normal to send impulses tb the eentral oflice, opens the line circuit# intermit-r fr tently for the same. purpose.' This opening of the circuit for producing the 'operating impulses is accomplished through the me dium of the impulse springs 6 and 7. y[t.-

will be understood, of course, that impulse v wheel is shown in Figfl in back view, the

dial being behind the impulse wheel` In Fig.- 3however, the reverse is the case.

When the subscriber removes his receiver;`

and closes the switchhook springs 3 .a'r1'd4,`v an energizing-*circuit is closed through the` line winding 8 ofthe line switcli C. ,The

current in this circuit, it will be seen, flows from ground G through the` line switch* springs 9 and`10'to 'the positive line conflit f se ductor 11, thence through thetelephone through the line winding 8 to the battery lead l?, and through battery B to ground Gr. As soon as the line winding S receives en'V 'ergizing current, the line armature 18 is lv"'attracted and the spring 19 is carried intoengagement with the ground spring 9. As a result a local energizing circuit is set up through the pull-in winding 2O of the line switch magnet. The current in this circuit, it -will be seen, flows from ground G through the springs 9 and 19, through thc pull-in winding 20, holding winding Q1 on the saine section of the vline switch magnet core with the line'winding 8, thence through the individual springs 2:2 and S23, and through the common springs 2e and Q5 to the battery lead l?, thence through hattery E to ground G. lll/'hen the pull-in winding 20 energizes, the plunger. armature :2G is attracted, and the line switch bank springs '27 and '28 are pressed into Contact as a result. By the same act the bank springs 29 and 30 are pressed into contact, and the springs 3l and 32 are pressed into contact, and the springs 33 and` 34e are pressed into Contact. Thebridge-cut-otf armature 35, which is a much lighter armature than the armature 26, is attracted at the same time with the armature 26; but its op eration is insured by the armature 26 which, upon being attracted, drives 'the bridge-cutoii' armature 35 to its attracted position. It will be understood, of course, that the plunger of the line switch C, at the time that the line switch C is energized, is Standing oppo site an idle trunl: line, which trunk line, it is assumed, in this instance is the trunk line running to the rst selector E. This trunk line, it should be stated, has a set ot' multiple contacts, not onlyin the line switch C, but in every other line switch ot the same group. The multiples are not shown, as itis not considered necessary. lt is through the'medium of these multiple contacts that the various line switches in the group controlled 'by the master switch D have access tothe irst selector E.

Y The master switch D is provided with a bank a having a number vof contacts equal 'to 'the number of trunks allotted the master switch to be presented to the line switches which it controls, one at a time. These con tacts are indicated at Common lto these contacts there is provided in the 'bank a a segment 36 Connected to the master switch relay 37. As indicated in the drawing, the

`contact in the baul; (l. representing the trunk which terminates in the selector l`is the contact- 38, and before the line switch C 0p crates, the master switch bank Wiper 39,

which is under the control of the master switch motor magnet 40, is in a position to connect the contact 38 with the segment 3G, thus maintaining the master switch relay 37 in connection with the conductor fil and with the multiple Contacty 34 and all other multiple contacts 34 of the group controlled by the master switch D one of which is provided for each line switch C. lt will be obvious that when the circuit is closed` by the bank springs 33 and 34, when the line switch C operates, the master switch relay 37 will energize. The current will flow` from ground G3 through said relay, through the master switch bank segment 36, wiper 39 and contact 33 to the conductor ll, thence through the line switch bank springs 34 and 33 to the battery lead 17, thence through battery B to ground G. The relay 3T, upon energizing, closes an energizing circuit through the motor magnet 40 by pressing the springs 42 and 43 into contact. The magnet 40 is vprovided with an interrupter arrangement comprising the springs and e5, so that it willv continue to energize intermittently as long as a circuit is maintained between the spring H and the battery lead 17. The arrangement shown is such that as soon as the magnet 40 energizes the first time, the springs 4G and 4T are pressed into contact by the cam wheel 4S and are maintained in contact until the master switch wiper 39 engages a contact b of the next idle trunk which, as shown, is the contact between the contacts 38 and 49. Of course, it is evident that had the trunk represented by this contact been busy, this contact would have been found connected to the battery lead 17, and the master switch would not have stopped on the contact 39a for the reason that, although the springs lr6 and 17 break contact as soon as the wiper 39 reaches the said contact in terinediate the contacts 38 and 49, and although the relay 37 denergizes as soon as the wiper 39 leaves the contact 38, the relay 37 again energizes as soon as the wiper strikes the said intermediate contact', if the said 'contact is connected to the battery lead as stated. O course, it is obviousthat under these conditions the master switch will not stop until a'contact b is found which is notguarded. If all of the trunks are busy, `then Ithe master switch D will continue to operate, thereby moving back and forth themaster switch wiper 39 and all idle-plungers in engagement With the shaft. The connection between the master switch wiper 39 `and the gear wheel 50, w ich is rigid with the cam 48, is not direc y. The wiper 39 is rigid with the plunger shaftthat is, the shaft which is engaged by all ofthe 'plungers When 'they are absolutely restored. 'The reciprocating faction between the 'gear wheel 50 and-theplnnger shattn'at 'i ou forked pivot. This arm may be moved in4 a. plane parallel to the plunger shaft, but. not in.,a plane at an angle thereto.

When the line switch C operates to press the ba'ik springs 31 vand 32 into contact, as

already explained, it Will be seen that a connection is established between the bridgecut-off winding 5l of the line switch magnet andthe spring 52 of the first selector E. It will presently be pointed out how, as soon as this circuit is established, the spring 53 is carried into engagement with the spring 52, and the Whole circuit set up through the bridge-cut-olE winding 51 for retaining the plunger arm 26 attracted. As soon as the bank springs 27 and' 2 8 on the negative side of the line, and the springs 29 and 30 on the positive side of the line,are pressed into contact, as described, an energizing circuit. is established through the line relay 54 of the rst selector E. The current in this en ergizing circuit flows from ground G2 through the Winding 55 of the line relay 54:, through the side switch wiper 56 in rst position) to the positive side of the line, thence through the telephone to the negative side of the line, through the side switch Wiper 57 (in irstposition), through the Winding 58 of the line relay 54 and to battery. The line relay 54, upon energizing, separates the springs 59 and 60, carrying the spring 66 into engagement with the 'spring' 61. An energizing circuit is, therefore, established through the slow-acting relay 62. It-Will be seen that current, Hows from ground G* through the springs 60 and 61, relay 62 and to battery. The relay 62, upon energizing, presses the springs 52 and 53 into contact, as already stated, thereby sending holding current through the bridge-cut-oi winding 51 of the line 'switch C. This current iiows from ground G5 through Ythe said springs 53 'and 52, conductor 63, line switch bank springs 32 and 31, bridgecut-oii'l winding 51 to battery. The armature 26 being already attracted, the energy supplied through medium of the Winding 51 'is suicient to retain it in the position shown While in this position, it will be 'seen that through the mediumof the bridge-cut-oifl armature 35 the springs 9 and 10 areseparatedpas Well as the springs 15 lind 16. `The object-"1n .separating 'these springs is to disconnect the line relay -winding 8 from acrosstheline. In order to., f insure vagainst av buzzing action 'rrhenjtliesprings 9, 10 and 15,16 are operated, the winding 21 is provided on that sec- 'bieaks the energizing circuitfor vthe l'ine ref lthe relay 62. This character is retained by :ing'and--soralled release. 'the private magnet relay 67 and the vertical 115 the first level vorder to retard the denergizing action of this part of the magnetof the lineswitch C, whereby the line armature'18 will not allowl the 'spring 19 tolle-ave the spring 9 before the first selector lli-has had time to press the springs 52 land 53 into contact. It will be i seen that When the armature 26 is in operated position, the winding 2l is short-circuited, thereby `rendering that section of the magnet sluggish 'for the purpose stated.` The slow-acting relay 62 of theirst selector E, upon energizing, not, only operates. the springs 52 and 53, but also-separates the springs 64 and 65, carrying the spring 65' into engagement with the spring 66,.wheref by connection is extended from the'spring 59 of the line relay 54 through the private magnet relay 67, and through said relay to the Vertical magnet 68.

Assuming, now, that the subscriber A desires connection with the subscriber- No. 1,110,he is ready to operate his dial by -putting his nger in the number 1 hole, drawf ing the dial down until his linger strikes the usual finger stop, and turning the dial loose. By thisoperation he 'causes the iinpulse wheel 5 to separate the impulse springs 6 and 7 once momentarily. In so doing he lay 54 ofthe first seclector E, thereby allowing the s'pring,A 6,0 to disengage from the spring 61, engage the spring 59, and return into engagement with the spring 61. Although the separation of the springs 60 and 61 breaks the energizing circuit of the relay 62, the armature of4 this relaydoes not tallv i back, because of the slow-acting character of slipping a spool of copper onto the core, as indicated by the square portion on the right.

The engagement of the springs 60and 59 sends an impulse through theprivate inagnet relay 67, which is also slow-acting, and '1 10 through the vertical ymagnet 68;- rent in this circuit iiows from The curground 'G "through 1 the springs 6 0 and '59 of the line relay 54,.spr1ngs 65 and 66 of the slow-actrelay 62, through magnet 68, side 4switch wiper. 69, (in first po- '-sition) to battery. By.: )energizing ,the vertical'magnet 68, the shaft ,of theselector E is raised verticallyone step, carrying the .lo

line wipers .70 and 71 andtheprivate wiper 72 up one stepsopposite the first contact of of the first selector bank- By this'operation.the-oi-nermal springs v73 and I 74 arepermittedtoengage as soon as the normal arm'A 75" attached to the shaft is 1 25 raised. By /theclosure 4`of .contact between these springsthe release'magnet '7 6 is placed in .connection with battery,so vthat wheneverr the release relay 62 E will be restored..`

denergizes, the switch` At the Sametime that the vertical magnet 68 energizes,.the private magnet relay 67 en; prgizes, closing the springs 77 and 78 into vfnuitact, `whereby a How 'of' current is sent' through the private magnet 79 from ground Gtthrough the said private magnet to'batk first selector. x`continues until the tirstidle trunk is found.

.ter.y. .Theprivate magnet relay 07, being sluggish in character, remains energized as long as impulses ar'e being sent in; 'but as soon as the impulsesfstop coming in, this relay Gihas enough time to denergizevwhieh in y turn denergizes the private magnet 79. The private magnet, of course, as is Well lmo\vn,'and through the medium of an escapement, nontrols theside switch comprising the side switch wipers 56, 5T, 69 and 80. With this arrangement, as soon as the private magnet 79 denergizes the first time. theside switch is allowed to pass to second position. One result of this operation is that a circuit is established lthrough 'the ro tary magnet 81 and the auxiliary relay 82. Current flows in this circuit from ground G2 through a set of interrupter springs 83, ro-

f'tary. magnet 81, coil 82, side switch 69 to battery. The rotary magnet 81 now, of course, as is Well known, intermittently energizes, rotating the selector' shaft step by step into engagement successively with the trunlrs running from the lirst level of the This step-bystep operation These trunks are, of course, protected by ground potential, and, if the iirst trunk is husy,' the private iviper 72 will be rotated onto a grounded contact, and an energizing circuit will be established through the private magnet 79 a second time, through the side switch wiper 80 in second position. The private magnet now holds its armature,

vwhich has been carried into attracted posi.

tion hy the armature of the rotary magnet S1, in the usual manner, as long as the private wiper 12 continues to find ground. Assoon 'i as the irst idle trunlr is found, the circuit thri'iugh the private magnet 79 is, of course, broken, and as the rotary armature returns toward normal position, after having advanced the private Wiper onto the idle trunk,

it permits the armature of the privatemag# net 'T9 to also return to normal, permitting fire side switch to escape to thirdfposition. By passing to third position, the side switch cuts the' calling line through to the sec ondary switch F, and disconnects everything from across the talking line at the selector E, which talking line comprises the conductors Si and S5 on the negativeside, and the conductors S6 and 87 on the positive side. But, it' the first trunk is idle, the rotary magnet, by depressing the armature ot'- the private mag once, trips the side switch to third position as the rotary armature falls back, cutting the line through to theiirst trunk. 0i course,as soon as the line relay 5.4 is cut od, it .denerizes and the springs return to normal, as shown; but the release'relay 62 does not denergize, because at thesanie time that the circuit is broken by t-he separationv of the springs 60 and 61 at ther line relayv 54, a holding circuit isset up through theA third position of the side switch 80 and trunk-release conductor 88 to the secondary switch FQ The Way this energizing circuit is set up is as follows: The" over the trunk-releasey conductor 88', through the magnet 92 of the secondary line switch F. This line switch, upon tripping, separates the springs 93 and 94, carrying the spring 94 into engagement with' the spring 95. The object of this arrangement is to disconnect the magnet 92l from the open 9 main spring 93, in order to prevent themagnet 92 from being denergized when the master switch H' operates. Of course, as soon as the secondary line switch F trips, a circuit is extended through the line relay 96 of the second selector L'Which causes the said relay to pull up. The current in this energizing circuit flows as. followsrrom ground G- through the lower winding of the 1 relay 96 and through the sideA switchY Wiper 97 (first position) to the positive side of the line, thence through the telephone to the negative side or the line, through the side switch wiper 98 (first position) and upper Winding of the relay96 to battery. The re lay 96 operates in a manner similar tov that l of the relay 5i of the first selector E, separating the springs 99 and 100, and carrying the spring 100 into engagement with the spring 101. The closure of these two springs 100 and 101 energizes the slow-acting release relay 102. rThe current in this last circuit flows from ground G7 through the springs 100 and 101 and through the release relay 102 to battery. One of the results .of energizing this relay is that the springs 103 and 10i are pressed into contact, thereby .grounding the trunk conductor 105.

The secondary line switch F, 'being similar in manner ot operation to the line switch C, uponv operating presses the springs 106 and 10".7 int-o Contact, as Well as the springs 108 vand-109, the springs 110 and 111, and the' springs 1'12 and 113, as shown. The springs f 108 and 109 being closed at the time that the conductor 105 is grounded, by the action of.

the relay 102, a locking circuit is set up for the magnet 92 of the secondary line switch The current through this locking circuit' flows from ground GS through the side switch Wiper 114 (first position), springs-108 and -101, secondary switch bank springs 109 and 108, through the secondary line switch magnet 92, springs 91 and 95 and resistance coil 115 to battery. -J ust about this time the slow-acting auxiliary relay 82 denergizes, extending the circuit from the slow-acting release relay 62 through the springs 89 and 90 of the relay 82 and side switch Wiper 80 (third position) to the trunkconductor 88, whereby the said release relay 62 is locked in multiple with the niagnet 92 of the sec* ondary switch F from ground GS.- It should be stated that the relay 82 is not quite as slow-acting as the relay 62 and denergizes in time to catch the relay 62 before the latter E falls back. Connection having been eX- tended to the second selector I, the calling subscher is now ready topperate his dial a second time for the hundreds digit-1. By operating his dial he again sends one impulse, as in the previous instance, thereby'operating the line relay 96, which is identical with the line relay 54 of the first selector E. As a result the private magnet relay 116 is also operated in series with-the vertical magnet 117,v

which are identical with the similar magnets 67 and 68 of the first selector E. The Vertical magnet 117, like the vertical magnet of the ir.-t selector,l raises the switch shaft to ,f theI proper level (the first level in this instance), and closes the circuit from the release 1nagnet`118 to battery through the oinormal'springs, as was done in the Afirst selector. The private magnet relay l11'6, ,inl

operating, operates in turn the private magnet 119, which is similar to the private mag net 79 of the first selector, whereby the second selector is caused to select an idle trunk line ruiming to a connector,and extend the circuit thereto as shown. It is assumed that and disconnects the line relay 96 from across the line. In falling hack, the line relay 96 separates the springs 100 and 101, and breaks the retaining circuit of the release relay 102 t atthis point. This also breaks the energizing circuit for the release relay 62 of thefirst selector, and' for the trip magnet of the secondary line switch Fgbut a new circuit provided through the side switch wiper 121' (third position), conductor 122, trunk conductor 123, connector release relay springs 132 and 131 to ground G15. This circuit is also dependent for its closure upon the energia-ation of the line relay 125 of the connector, which occurs at the instant that connection is established With the said connector. It should here be stated that, vif

necessary, th'e magnet of tlieline switch F may also be made a little slow-acting'in' order to insure that the connection shall not he broken while the ground 'is being shifted y from one point to another.

The line relay 125 of the connector havy ing pressed the springs 12iand 126 into cony tact, causes an energizing circuit t0 be established through the slow-acting release relay .127. This relay 127 thereupon separates the springs 12S and 129, and carries the spring 129 into engagement with the spring 130,

into contact.

The subscriber at the calling digit 1. In so doing the energizing circuit of the line relay 125 is interrupted oncem It will he Seen that in the' usual manner.

sa and the springs 131 and 132 are also carried' stationvis `now ready to operate his dial for the tens.

this energizing circuit the current fiowsfrom ground G10 through 'the lower winding o# the relay 125 tothe positive side-1330i thevl talking line, thence through the telephone to the negativesidc of the line, throughcou ductor 184, and through the upper Winding l of the relay 125 to battery. The impulse transmitted by the subscriber A allows the relay 125.t0 fall back once, thereby .permit-j ting ythe spring 126 to fall into engagement ioo with the spring 135. As a result an en'ergizy ing circuit is closed through the vertical @magnet 136. said circuit extending from l ground G9 through the springs 126 and 135 of the line relay 125, thence through the springs 129 and 130 of the slow-acting re lease relay 127, and through the ,vertical magnet 13G, side` switch wiper 137 (first position) ,i and slow-acting private magnet relay 138 to battery. The vertical magnet 136 operates just as thevertical magnet in the selectors, raising tlie'switch shaft one step, thereby raising the shaft Wipers opposite the' first contact of the first bank level.

At the same tiinethe off-normal springs 139 and 140 are closed;in contact'.,therehy con-` necting therelease magnet 141a to battery. At the rsame time that the yertical magnet energizes, disconnecting the springs: 141 and 142 and pressing the spring,142 1ntoengage-- ment with the spring 143, and the spring 4 144 is also disconnected. from "the spring 143.

By closing the'springs 142 and 143 an energiz-ing circuit is established through the private magnet 145. Current through this 'cir cuit, it will beseen, flowsftromy ground G11 through the said springs l,and A through the,

12a 136 energizes, the.;piivate magnet relay138 y 146 instead oithroug cuitis maintained by Way of the springs ineens@ private magnet 145 to battery. The private magnet therefore energizes and remains ens ergized while the impulses are being sent in through the vertical magnet-136. However, as soon :is theim'pulses cease to come in, the private magnet relay 1318 denergizes and breaks the circuit of theiprivate magnet 1115, at which instentithe side switch passes to second position. The calling subscriber is nonv ready to send in the last set of impulses for the digit 0 of the desired number. Again, the line relay 12d is operated, in this instance ten times. p The side, switch wiper 13'? having been shifted to second position, the impulses due to the closure of Contact between the springs relay l'pass throug the rotary magnet 136. By the operation of the rotery'rnagnet the vshaft Wipers are carried into engagement with the `lline contacts of the desired line. The-private magnet relay 138 is again'main# tained energized While the impulses are being sont through the rotary magnet 1116. Wh'enithe impulses cease tocorne in,^however, the 'relay 13th-fes inthe previous instance, falls hack, breaking the circuit through the private magnet 145 the culled line is not busy, und permitting the side 'switch to pass to third osition. It will be seen, however, `that if tlie` called line is busy, the private wiper 147 Jwill encounter e ground potential, whereby "the energizing circuitoi the private in'agnetA 145 is, maintained eren utter the spring A14:2 lea-Ves the spring 143. This eir- 142 and 141'," and; is not broken when thc spring 142 shiftsfrom the spring 143 to the spring 1111, bec' usethese three springs are permitted t engage for a short interval. ThisA holding circuit continues through the side switch Y Wiper 118v (in second positionl through the ringer reluv springs 149 and150. through'the lower Winding 151 of the backbridgc double-Wound coil 1.52, through the springs land 15s of the ,auxiliary relay 155 to the private Wiper 147 und to ground. Since this' locking circuit for the private magnet 1515 contains one Winding of the relay 152, the relay 152 will energize, and it iu turn cnergizes the auxiliary relay 155 which gives the busy signul to the calling lino. The sir'lesu'itch lic-ing unuhle to pass to third position, the culling subscriber 'is prevented troni connecting his own line with lthe desired. but busy. line. ,lt will be seen thut this locking circuit for the private niagnet 1-15 is shifted from the private Wiper to the ground Gli us soon ns the. auxiliary relay 155 encrgics. the culled subscriber is not busy, however, connection is established us explained. and the interrupter 156 intermittently onergizes the ringer relay 157, which continues to send ringing current periodi cally to the celled line until the called sub- `is energized, hre-airing the circuit of 13,25 and 126 of the line the vertical magnet:

` if. the calling-- et which time the relay 152 the ringer relay`157at the springs 1563. The energizing circuit of the relay 15'? extends from ground through the interrupter 156, springs 156,

soriber answers,

relay 157,' side switch wiperV 137 und relay 13S tofthe buttery lead 1l'.

The relay 152 is energized by the talking battery current or' theV called substation, which current flows from ground G13 through the side switch Wiper '159, 'lower Winding of the relay 152, thence over the heavy talking conductors yto und through the substation K and buck side ot the line rand through the upper winding of the relay 152 to the battery lead 17. The relay 138 is not energized over this circuitA due to the comparatively 'high resistance of the ringing relay. j

It will also be seen that 'as soon as the Vside switch of the connector passes to third position, a ground guarding potential is applied to the private Wiperl/l? from ground G13, through the side switch wiper 159 andthe springs 153 and 154 of the relay 155. This guanding potential protects the called line from being called by anyone else and sends a llow' of current through the bridge-cut-otl Winding 160 olf, the culled subscrihers line switch C, which irinding1 upon being excitcdfattracts the hridge-cutotl armature 161` thus disconnecting the line winding 162. from the line. y

After the subscribers 'are througl'i talking,

subscriber hangs up his receiver, -he opens his line and thereby causes the line relay 125 of the connector to del energize and. asma result, the slow-acting release relay 1'271rle'e'nergizes also. The former relay 125 Tits oil' ground from the conductor 123 hy separatiiuT the springs 126 and 125e, thereby permitting the lrelease relay 162 of the second selector' todenergize, also the trip magnet Sil of the seconillary line switch F and the release relay 69 of the first selector 1G. The release relay 102 of the second selector l, upon decncrgizing, closes n circuit through the 'release magnet 11S Aby permitting the springs 163 and 161 to engage. The current through this energizing orer the other onergizcs. thc plunger arm 16T is res-termi.

the springs J5 und '1li ure scpuruled and the spring Sli reingages the spring 93. The rep .lease relay 62 oflthe" selector'E-iupondej energizing, operates in ay manner similar to th releaserelay 102 of ther-*Lecond selectcr'f fuses the' release of the first selector E' Aan bye rgia'ing'the release magnet 176. The e er luigi current for said Vrelease magnet fll'dws'rpmground G? throughj the 'springs 60? and 59, through the springs 65" amd64,

-release magneti? 6. and olf-normal springs 74 and. 7 3-to battery." rflic g release relay 62 of the first selector E, upon "falling back,v also permits the springs 52 and 53' to separate,

thereby breaking the holding circuitthrcmgl'i the bridge-cutoff Winding l51 ot` the ,line switch Cer'atwhich time the' line switch Crestores tojnormil. In the meantime therelease'relay 127 'of -the'connector falls back, carrying the springs 128 'and 129 into enga gement, thereby closing the circuit through the -release, magnet 141B. Current in this circuit liowsrom ground G9 through the line vrelay springs 126 'and 135,.thr'ough the 160 of the line switch C is broken, andthe' line switch -C is normal position.

By referring to the master switch D in Fig.'-1 it will be seenthat the motor magpermitted to assume its net 40 has a slowacting relay 168 in multiple. therewith.`v This relay is adapted to p remain energized and retain the main springs 24;, and 25 open While the master switch is` 'rotating'. The function fathese springs'is to prevent a subscriber from con-l necting with a busy trunk should a sublse lscriber remove his receiver'while the master switch is rotating. In carrying out my nvention I provideqa relay 169 which is de-A signed to be inserted between the pull-in winding 20 of the line switch and the battery lead whenever the said 4springs 24 and 25 are separated. The relay 169, when energized, presses the ,springs 170 and 171 into contact, thereby putting battery current on the slow-acting relay 172 through its springs 173 and 174. It should be stated that the j spring 173 is a multiple spring, there being as many springs 173 connected with the spring 171fas there are line switches. Also,

it should be stated that the relay 169 is a relay common. to a group. Therefore, if

any subscriber removes his receiver whileA the springs 24; and 25 are separated, the'` relay 169 will energize as aresult of the attraction of the line amature 18 of the subscriber who has thus removed his receiver.

This energizing circuit may be traced from ground G at the line switch C through the springs 9 and 19, through the'opull-in Winding 20, winding 21, springs 2,2 and 23, relay 169 to battery. The relay 169-is'af high resistance relay, so that not enoughcurrent is permitted to pass through the winding 20 of the line switch to operatively energize the same. The relay 169, being energized, and:

the v'armature 18 being attracted at the same time, an energizing circuitis closed throu h f u through the springs 9 and 19, through the theslow-acting relay 172from ground f said relay 172, and through the springs 174 l and 173 andv springs 171 and.' 170 to battery. f The relay 172, upon energizing, disconnects itself' from the spri g 171 by shifting the spring 174: from the spring 173,' and locks itself onto main battery direct by cariying i' i i the spring'174 into engagement with the spring 175. l At the same time the relay 172, y

by separating the' springs 22 and 23, opens ssi the circuit o'f the pull-1n magnet 20 at a point which is retained open as longas the relay 172 is retained energized. It will ber seen that when the spring 22 separates from y the spring 23 it is carried into engagement with the busy spring 176. Thus acircuit is closed from the battery lead 17 through the secondary winding of the busysignalingmachine, springs 176 and 22, windings`21 and 20 andA sprlngs 19 and 9 to ground G',

thence back through the battery to the starting point. The battery current flowing over c this circuit is not suiiicient to operatively` A energize the winding 20, but the alternating 'current produced by the busy signaling machine, in passing through the winding ,21,l

induces a busy signal in the winding'B,

which signal is carried to the subscribers telephone. Upon hearing' the signal the subscriber hangs up, and thereby opens his line fall back. Asa result the-energizing ciro cuit through the rrelay 172 is' broken and f permits the said relay to restore to normal, again connecting the pull-in magnet 20 to the springv 211 and its own coil to the open f main spring 171. It will be obvious that the Y relay 169 will cause as lmany relays 172 to energize, when it pulls up, as there may be subscribers inthe group who removeA their 1v receivers while the springs 24 and 25` areseparated.' It will be seen, therefore, that any subscriber who removes hisreceiver while the master switchfis rotating will'be 26 locked onglbusy and kept there until he hangs up. In this way two or more sub' scribers, who may have lremoved their.rev

ceivers while themaster switch is moving,

will not plunge into the same trunk at the instant that the master switch stops.

' At the 'secondary line switch F the arrangement is as follows: The motor magnet relay 177 is, as in themaster switchD, multipledvby the relay 178, so that while the Q masterswitchis moving, the relay 17 8. is en- 10511 i circuit, whichpermit's the armature 18 toA f masses ergized, whereby the springs 1719 and '180 are separated to prevent` Vany secondary switch F from tripping while the, master 'switch is rotating. 1i, while thegsprings 179, and 180 are separaed,..connectien is established with the trunk terminating in the secondary syvitch F, the auxiliaryrelay 181 is energized by the saine current which.

' ground G14 through the springs 185 and 186, through the springs 189 and190, winding 191, springs 192 and 193 to the positive side of the line, thence through the telephone and back to the negative side of the line, whence the circuit is continued -to the springs 194 and 195, through the windin 196, springs 197 and 198 and springs-'18 and 188 to battery. The rela 184:, upon energizing, disconnects itself'. from -the springs 186 and 187, and connects itself with 3e' the positive and negativeterminals` of the battery direct, Under this condition the busy current which is passing through the winding 201 is induced. in thev line, and the calling subscriber is given the busy signai.

It will be seen that the relayl 181, by pressingithe spring 182 onto the spring 202, aiso giqllnds the trunk conductor 88 for holding up` the first selector E. When they calling subscriber hears the busy signal he hangs 40 up his receiver, opens the line and permits the relay 18e to fall back, which thereupon restores and permits the 4release of the switches E and C. 1t will be seen that the relay 184, while energized, holds the springs 182 and 183 se arated, thereby making it impossible ,for tne pull-in magnet 92 toenergizeafter the open main springs 15'? SF' and 180 rengage, and before' the calling subscriber releases. It is thus seen how a 'secondary line switch is. locked on busy and heldthere if a calling subscriber'should cbtain connection 'therewith while the master a switch is operating. `It will be understood, of course, that the' master switch H isthe, ff'same as 'the master switch l) and is ed- V'anced each time that a trunk is seized, zas,

for example, when a trunk to the secoi'ilA selector is seized. This, of course, is .donef by the closure of contact betweenthe bank.

50 springs 110 and 111, ex'aetly asjwas done in the master switch D. .f v

It is obvious that in asystenrof the character described the subscribers switches may aloneibe provided with the means herein described, in which case the relav 18e ofthe 'ondary switches are' discarded, the trunk secondary switch F would be discarded, the springs 182 and 183 short-circuited, and the relay 181 also discarded; likewise, the springs 194 and 195 vand 192 and 193 will be discarded? Likewise, in this system the secondary switches alone might be provided with the arrangement whereby they may be J locked on the busy apparatus, if seized while the master switch is operating, in which case the relays 172 and 169 would be discarded and the springs 22 and 23 shortcircuited. Itis also obvious that the systern niay operate without secondary switches F, or without line switches C. If the sec- S0 conductors 199, 200 and 88 would be a continuation of the conductors 203, 212e and 105. in case the line switches C are discarded, each subscriber would be provided with a selector switch E, normal conductors, such as the normal conductors 205, 205 and 207, and a bridge-cubed relay, corresponding to the winding 51, which would be adapted to disconnect the line relay ed from the line when the line-is celled. The springs 52 and 53 might, of course, be discarded. In a systeni using Keith switches it is sometimes v customary to insert a relay between the spring 241 and the lead 208, as shown in Fig. 6. Such a relay is common to the subscribers of the group, and is adapted to close. a local energizing circuit fthrough a second relay, slow-acting in character, which operates a ten point side switch. Each one of these points is connected to a corresponding trunk conductor 63 running from the line switch to the next switch. The arrangement is such that normally the conductors 6 3 are disconnected from each other, but as soon as the relay pulls up, all or" these conductors are grounded until the slow-acting relay denergizes., Said relay, of course, deenergizes as soon as the circuit 1s opened through the pull-in winding 20. This insures the action of the line switch C-that is, it insures that the line switch C will not fall back, because of the possible siow` action, for exampie, of the line relay-.54, and Vof the slow-acting relay 62. The 4saine arrangement is applicable to the secondary switches F. The first relay wouldbe inserted in the circuit connecting the spring 179 with the spring 93.. This relay would close the circuit of the slow-acting relay 62, and trip winding 92 until the relay 102 pulls up. i

My invention is, therefore, applicable to a two-wire system for thepurpose of prel Venting-subscribers from interfering with each other by attempting to make a call 125 Y while the master. switch of the callin sub.-

scriber is in'operation. lt is applica le to a two-wiresystem for preventing subscribers from interfering witheach other by attempting [to call through secondary line 159 switches while the'controlling master switch is in operation.

My inventlon provides means for eiciently holding a subscriber, either at a line switch or at a secondary switch, if he has attempted to passa call through either while the controlling master switch of either is -in operation. And it also provides means for giving the subscriber a signal when thus locked, whereby he may restore his apparatus and call again. l

What I claim as my invention is 1. In a telephone system, a calling sub- 'scribers line, a called subscribers line,

,the lirst switch causes the 'operation of said common mechanism, the said second switch is rendered inoperative for calling while the common mechanism 1s operating, and means whereby, it an-attempt is'made to use the said second switch for calling, the call is blocked and a-signal given to the calling party indicating that he cannot get his call' and should release.

2. A subscribers' linen; switch for calling` purposes adapted begusedby said line, a controlling device .fo' said switch, said controlling device adapted to be operated, means'uwherebl while the said controlling device is operated, `the said switch is rendered inoperativeor calling, together with means whereby, if an attempt is .made to is blocked and the subscriber is givenasig- Y make a call through the said switch, thecall nal indicating that he cannot get his call and should release.

In a telcphonesystemfa switch forv calling purposes, a device for controlling said switch, means for.operating saiddevice, means for rendering the said switch' incapable of transmitting a call while 'the device isloperating, together 'withm'ean's whereby,vif an attempt is made to use -the said switch for calling while the said device' is operating, the calling party is signaled 'to LI-n a telephonesy'stem, la subseribers" line, a switch for said line for. establishing-'- connection withl another line, an 'operating magnet for closmg said connection,"a controlling master switch adaptedto operg ated when'such a' connection is'made Aby said switch, or `by some other switch, means for rendering the said operating'ma'gnet .in-

operative Whilethe master "switch 1s o er ating, together with means whereby,ri an attempt is madepto operatethe said opera@ ing magnet, the 'first-mentioned. switch is locked and made unresponsive'to a call until i the switch is released.V

5. In a telephone-system, a.. switch .for 04k establishing connection vbetween two lines, fqf* an auxiliary switching mechanism adaptedI to be operated, means for.,v rendering saidswitchv inoperative for connecting purposes while the said auxiliary 'mechanism is 111171521.;

operation, together with means for preventing the said switch from becoming operative `for calling purposes as soon as the auxiliary i' mechanism stops itsfoperationnif an attempt has' been made to use the saidwfswitch for connecting -purposes while the auxiliaryl ,mechanism was'op'eratlng.

6. In a telephone system, a line, a switch adapted to be operatedy from said line for llvcalling purposes, an auxiliary' switchinglgfy mechanism adapted t?) bejoperated', means for rendering the Asaid Switch inoperative for 1 callin` while the aukyiliary rmechanism is opera ing, together with means forfpnevent# f ing the said switch from'becoming operative fv for calllng-:purp'osesas soon' as the auxiliary mechanism stops its; operation after Van ati f tempt has been made romsaidline to use f the said switch Yqr; calling purposes' while'. Y

` thev auxiliary mechanism was operating, and c5 means for signalingthe subscriber who 'at" tempted the call that he has failed to make f' l the 'connectiom 7. In a telephone system', subscribers??` l lines, an individual trunln'ng switch for eaclrfioo j line, a master switch for controlling said in dlilvidual switehesfadapted to'select trunks a e `the'fevent thatv twoormore subscribers callat the lsame timefandfwhile thel master* switch "is: in operation, 1 to prevent' seizure of y the same trunk by 'ft-woor more subscribers:

VYS'. In a telephon system, la pluralityoff lines, an individuai trunkng switch for each` l line, a master switch "controllinghsaid indi- '11n f vidual switches,l adapted to select trunksl "7"" ahead ,of the'calls, trunks leading from said` switches, numerical switches '.at the other K' ends of said trunks, and means operative in i L vthe event that two 'or more subscriberscall 115k' subscbers jupes, inaiviauntm ad of the calls, and meansoperative in'` switch for each line, a' master switch -controlling sai-d individual switches, an o erating magnet for said trunhing switc an energizing `circuit for said magnet' includ; ing a pair ci contacts, a relay for controL ling said contacts, vmeans for maintaining said relay l energized while said master .switch is operating, a second relay connected in shunt of said contacts for controlling said switch, and'rneans for energizing said l second relay if a subscriber takes o his receiyer while said contacts are separated by' .the energization of said first-mentioned relay. c

11u. ln a telephone system 4a pluralit of subscribers lines, an individual truning switch for each line, a master switch controllingv said individual switches, an operating magnet kfor said trunking switch, a pair o relaycontrolledcontacts in the energizing circuits for saidmagnet, a second relay in shunt of said contacts, aand a third controlling relay adapted to he energized when saidcperatiug magnet and second relay are energized at the l,same time. i

l2. En a telephone system, subscribers lines, an individual t'unlnng switch for each line, a master switch controllingy said indiof said trun controlled by said mster switch, a relay in shunt ci said contacts, a second relay controlled hy said last-mentioned relay, and means controlled by said scond relay for controllingthe operation ci said trunlring switch.

' le. n a .telephone system', subscribers lines, individual non-numerical `trunliin switches foreach of said lines, amaster switch controlling a plurality of said indi- -vidual switches, a relay controlling the operative connection oi said trnnking switches to said subscribers lines, means for energiz` ing said relay over a circuit including a contact common to aplu'rality of said trunking switches, and means for ,locking said relay over `an individual local circuit.

15:@ va telephone system, subscribers lines, an individual non-numerical trunking switch for-each line, armaster switch 'con- Ivtrolling a y lurality "hf 'such trunkin switches, an@ generating, magnet for contacts conftrunking switch, apair of contacts common to a plurality of said switches and a pair of contacts individual to each switch, and an energizing circuit for said operatin magnet including said common and individual contacts.

'16. In a telephone' system, subscribers lines, an individual non-numerical trunking switch for each line, a master. switch controlling a plurality of such trunking switches, an operating magnet for said trunking switch, a pair of contacts common to a plurality of said switches and a pair of contacts individual to each switch, an energizing circuit for said operating magnet in cluding said common and individual contacts, means for closing said common contacts, and means for maintaining said individual contactsopen after said common contacts are closed.

17. In telephone system, a non-numerical trunliing switch, a ulaster switch cntrolling ya, plurality of such trunking switches, an operating magnetAv for said trunking switch, a 'line relayrfor sd switch, a, Second relay iinder the control of said maSv ter switch, a third relay controllingthe circuit of said operating magnet, `and means whereby Said third relay lwill be energized if said line iela'y is energized while said second relay is energized. 3-

18. in a rtelephone*system, subscribers lines, an individual trunking switch for each line, a plurality of secondary trunking switches, a master switch for controlling said secondary switches, adapted to select trunks ahead of the calls, and means to pre' vent seizure of the Same trunk by two or more secondary switches while said master switch is operating.

19. In. a telephone system, a plurality of linesan individual trunlring switch for each line,.`a master 'switchcontrolling said individuarl switches, adapted yto select trunks ahead of the calls, trunks leading from said switches, numerica-l switches at the other ends of said trunks, means operative in the los eventthat two or more subscribers call at Y the same time, and while the-master switch is in operation, to prevent seizure of the same numerical sw1tch by two or more subscribers, secondary nonnumerical switches with which said numerical switches connect, adapted to select an idle trunk, .and means V for preventing two orv more of said secondary switches from seizing the Same trunkf" 20. ln latelephone system, a plurality ciA trunk lines, non-numerical trunking switches, a master switch for lcontrolling said nonnnmerical switches adapted to select trunks by one ofY said switches.

flle'lu'atelephoue system, a pluiiality` of,

v12a` ahead of the calls, and means to iprevent` y at notget his call and should lrelease.

fil-Q trunk mesma-numerical trunlng al masterswitch for controlling 'said nonb numerical switches adapted t'oselect trunks ahead of the calls, and -I'neans to prevent seizure of a trunk by\ ther of said 'non-y numerical switches when it has been seized by one offsaid switchesand while saidmaster 'switch is in operation.

22. In a telephone system, a callingl'sub- 1i,tsc1'ibei"s line, a, called subscribers iine, means "fori extending a connection between. "said" lines, including a switch, a second calling subscribers line,'a second called subscribers line, means for extending connection be; tween'the said second lines, also including a second switch, a common controlling mechanism for both'of said switches, a controililx'g circuit for said common mechanism common to said switches and Ameans for closing 'said controlling circuit when any one of 'said switches is operated for operating the common mechanism, together with means whereby, when the rst switch causes the 'operation og said common mechanism, the'said second switch is rendered inoperative for calling while the common mechanism is operating, and means whereby, if an attempt is made to usci-the said second switch for calling, the call is blocked and a signal given to the calling party indicating that he can- 23.- A subscribeLi-s line, a progressively movable trunking switch under 'the control of the said line through the medium of suitable circuits, a device for controlling vthe -progressive motion of vsaid switch,'electro wgnagnetic 'means for operating said device,- said circuits under the control of said device for rendering the switch inoperative while the device is in operation, together with means whereby, if an attempt is made to make a'call through the saidswitch, the call is blocked andthe subscriber is given a signal indicating that'he cannot get his call and should release,

24. In a telephone system, a subscribers line, a switch for said 'line 'for esttblishing conectionwith anotherI line, an operating magnet for closing said connection, a controlling master switch, means for operating said master switch `when a connection is made by said line switch, means for render-A is released.

ing the said operating 'magnet inoperative while' the master switch is operating, to-

gether with means whereby, if an attempt is made to operate the said operating magnet, the first mentioned switch is locked and made unresponsive to a ca'll until the switch 25. In a'telphone system, 'a switch vfor establishing connection .between two lines, an auxiliary switcliing mechanism, means for `operating saidl switching mechanism when av connection is established, means forrelidering said switch inoperative 'for conn'ctin'g purposes while the-said auxiliary mechanism is lin operation, together withv f' means for preventing the said switch from becoming-operative or calling purposes as soon as the auxiliary mechanism stopsy its o eration if an attempt has been made/'to use t e 'said rswitch 'for connecting Vr'iurpos'es while the auxiliary mechanism was operat- 26. i[n a telephone system, a line, a vparogressivei'y movable switch for said line controlled thereover .for calling Apurposes through the 'medium ofsuitable circuits, an Y auxiliary automatic electromagnetic mechamsm "for controlling the progressive Y movements of sald switch, means for operating said mechanism comprising suitable circuits under the .control of ysaid l'pro. ,'ressively movable switch, said auxiliary mechanism controlling the circuits of vsaid` progressively movable switch to render theswitch inoper-` 'ative for calling purposes when the auxillines, a progressively movable trunkin-g switch for each line, each switch controlled over its own line through the medium of suitable circuitsfa master `switch for confv trolling lthe progressive movements ofsaid switch, trunks associatedV with said individ-f-- l l ual switches and with said selector switch, bus test circuits for said trunks,-,means for app 'ying a busypotential to said"busy testv circuits when they are brought into use,

means for initiating the operation 'ot said?, master switch when a call is made and means for `continuing the operation of saidY master 'switch comprising said busy test circuit'for locatingfan idle trunk for the next call, and means operative in the event thatrv two or more subscribers call t the same time, and while the master switch is in opiis eration, to prevent seizure of the same trunk by two or more subscribers. i

28. In a 'telephone system, a plurality'oi lines, a progressively movable trunkin switch for each line, each .switch controlled over its own line through .the medium of suitable circuits, a master switch for conw;

switch, 'trunks associated with said individual -switches and with said'inaster switch,-

' means for initial; ng the operation of said trolling the progressive movements ofsaid" call, saidltrunksleading from switches,

\ masterswitch comprisingsaid busy test circuits for locating an idle trunk for `the next numerical switches at the other ends ofsaid trunks, and means operative in the event l that two or more subscribers call at the'same 'ti-me, and While the master switch is op- Illinois, this 24hv eration, to prevent seizure oi fine Asaine 19 numerical switch by two or ignor subscrib ers. f v

.Signed by me et Chicago; Cook county,

lday of March, 1909.

EDWARD D. FALES.

Witnesses:

ETHEL A. Enom, Y ARTHUR J. RAY. 

